1. Field of the Invention
The present invention relates to a detect/modulate circuit, and more particularly to a detect/modulate circuit using transistor switches to modulate a bandgap.
2. Description of Related Art
As the semiconductor design becomes a mainstream of the present semiconductor industry, the development of 3C and system-on-chip (SOC) becomes very popular under this trend. If low price, high performance, power saving, light, thin, short, compact and portability are taken into consideration, a more precise design technology accompanied with a better manufacturing process can achieve the request. At present, the number of transistors in per unit chip is increasing, and the integration of different elements is a significant achievement made by chip developers.
For all integrated circuits, a bandgap is needed to produce a reference voltage. The bandgap is to provide a stable temperature and voltage changed voltage. However, the bandgap will produce a deviation of output voltage due to a change of semiconductor process. To solve such output voltage deviation, related manufacturers adopt a plurality of small resistors connected to a main resistor in series. Referring to FIGS. 1 and 2, in order to compensate the deviation of output voltage, a fine tuning circuit B is connected to a main resistor A1 of a bandgap A in series, and the fine tuning circuit B includes a plurality of resistors B1 connected to the main resistor A1 in series, and each resistor B1 is connected to a fuse B2 in parallel, such that each resistor B1 is used for fine tuning the absolute value of the main resistor A1. The fine tuning is achieved based on whether or not the fuse B2 connected to each resistor B1 in parallel is fused.
But the aforesaid prior art bandgap has numerous drawback as following.
1. After the bandgap A is fabricated in a chip. To achieve both positive and negative fine tunings, all fuses B2 are not fused (short-circuited) before the chip is processed. So the voltage A2 of the bandgap A must be too low (as shown in FIG. 2).
2. The prior art fuse B2 uses a current for fusing. When the current is controlled improperly, the bandgap A will be damaged, and thus the bandgap A will lose the function.